In many computer systems, system power specification is based upon analytical models. Such analytical models make certain assumptions on distribution of power usage by various components of the system. The system power specification is sum of maximum estimated power consumption of all the components. A system power supply is designed to support this system power specification.
Typically, there is no protection against power supply or system failure due to over demand of power by the components in the system. For many computer systems, it is impossible to measure power usage in all the possible scenarios. In addition, many new usage models, applications and data patterns are discovered on regular basis. When a new usage model makes the system components demand more power than what the power supply can provide, the power supply and accordingly the system fail. To reduce probability of failure due to component power specifications, voltage regulators (VR), power rails and power supply are designed with hefty guard banding (e.g., over designed). For example, a system power supply may have a maximum rating that is a percentage (e.g., 20 percent) higher than the system power specification.
When the power supply solutions are over designed, there are two major problems. First, the inflated system power specification drives higher demand on associated infrastructures. These problems are more evident in data centers. For example, in data centers, systems are installed on racks. The racks have limited power and cooling capability. Many times data center administrators use system power specification (based on name plate specification) to determine the number of systems that can go on a rack. With system power specification growing every generation, the number of systems that can be supported by the rack decreases. As a result, there are more and more empty spaces on the rack. Second, an over design results in larger and more expensive power supply and voltage regulators.